This invention relates to working fluids for use in absorption refrigeration systems. More particularly, this invention relates to compositions useful as absorption refrigeration working fluids which are inhibited in the corrosion of the internal metal surfaces of the system, and to a method for retarding corrosion of ferrous metal surfaces by concentrated salt solutions.
The working fluids employed in most large commercial absorption refrigeration systems are concentrated aqueous solutions of lithium bromide. Corrosion inhibitors such as arsenic trioxide have been successfully employed in these aqueous systems to prevent corrosion of the system at working temperatures of 250.degree. F. and higher. Systems employing these aqueous working fluids are widely known, and are further disclosed and described, for example, in U.S. Pat. No. 3,555,841.
Alternative working fluids have also been sought which would permit the use of higher absorber temperatures while maintaining the same low vapor pressure and refrigerant temperatures. Aqueous systems generally require that large volumes of water be employed to externally cool the absorber since the absorber must be maintained at a temperature sufficiently low (at constant pressure) to prevent crystallization of the working fluid. An alternative working fluid which could operate at a higher temperature would permit the use of air as the external coolant, thereby eliminating the need for large volumes of chilled water and/or cooling towers. Among the possible compositions useful as alternative working fluids are those based on alcohol solutions of lithium bromide or mixtures of lithium bromide and zinc bromide such as those disclosed by Hainsworth in "Refrigerants and Absorbants", Refrigeration Engineering 48 97 (1944). These working fluids would appear likely to permit the use of higher absorber temperatures and consequently allow replacement of the external water coolant by air.
A further problem which would be rectified by the use of alcohol-based coolants is that of freezing. Water-based working fluids tend to freeze up at environmental temperatures commonly encountered in the field. Alcohol-based fluids would prevent such freeze-ups during warehousing, and additionally allow the absorber units to be installed outside the structures being refrigerated or cooled. It is thought that such systems would have utility in residential as well as commercial applications, and would permit the design of both fuel-fired and solar-heated devices.
Alcohol-lithium bromide-zinc bromide working fluids are quite corrosive to the ferrous metals commonly employed in the construction of absorption refrigeration systems. While the use of exotic metals may be used to overcome corrosion problems, such constructions are neither economical nor practical for wide application, and the use of alcohol-lithium bromide-zinc bromide working fluids would thus be severely limited. An effective corrosion inhibitor for these working fluids is thus clearly needed if they are to find application in practical absorption refrigeration systems.